WO2009105441A1

WO2009105441A1 - Method of manufacturing carbon-rich product and co-products

Info

Publication number: WO2009105441A1
Application number: PCT/US2009/034356
Authority: WO
Inventors: Srivats Srinivasachar
Original assignee: Srivats Srinivasachar
Priority date: 2008-02-19
Filing date: 2009-02-18
Publication date: 2009-08-27
Also published as: CA2716190A1

Abstract

A method (10) of manufacturing a carbon-rich product and co-products. A parent hydrocarbon-rich material such as coal is provided (24). The parent material is processed (26) so as to produce both a carbon-rich solid material such as activated carbon that has a higher carbon to hydrogen ratio that that of the parent material, and a hydrogen-rich combustible gas that has a lower carbon to hydrogen ration than the parent material. The process includes activating the material by exposing it to a hot gas stream having elevated levels of one or both of carbon dioxide and water vapor. The combustible gas is combusted (32) to produce heat. At least about 40% of the energy content of the combustible gas is used in a separate process (50, 90, 90a, 110, 110a, 110b, 150) having one or more endothermic steps.

Description

METHOD OF MANUFACTURING CARBON-RICH PRODUCT AND CO-PRODUCTS

FIELD OF THE INVENTION

The present invention relates generally to the production of a carbon-rich product (e.g. activated carbon) from a hydrocarbon material such as coal and/or biomass with the generation of excess energy and the generation of a co-product which utilizes the excess energy for its production.

BACKGROUND OF THE INVENTION

Many industrial processes require energy for one or more process steps. A typical energy demand is for material drying or water evaporation. Another typical demand is for process heating, to effect either a physical and/or chemical change, such as calcination of limestone to lime in cement clinker production. Most industrial processes use natural gas or fuel oil for process heat or steam production. Natural gas and fuel oil are premium fuels whose prices fluctuate significantly and are also high-priced. Solid fuels such as coal are a low-cost alternate that can be used is several cases for the same purpose. However, there are operational challenges with using coal, either via combustion or gasification, because of the increased carbon dioxide emissions relative to natural gas and also because of the ash in the coal that causes operational problems such as deposition and fouling of heat transfer surfaces. A new way of using coal for process heating applications or steam generation is required, which will minimize operational issues while at the same time minimize the increase of the carbon footprint (carbon dioxide emissions).

Additionally, the use of solid fuel for energy generation, while resulting in lower operating costs, requires equipment that is more expensive than when using clean fuels such as natural gas. When using a solid fuel, a higher return on capital investment is required via the simultaneous generation of alternate products that carry a higher economic value than just energy supply.

Several carbon-rich products have economic value and end-use applications. These include but are not limited to the following: activated carbon and activated charcoal for various gas cleaning and liquid processing applications; carbon-rich solids that can be used for soil amendment or as carriers of fertilizing compounds for slow-release into the environment; ultrahigh surface area carbons for ultra-capacitors; and porous carbons for gas storage or gas separation. The activated carbon used for such applications is manufactured from hydrocarbon materials like coal or coconut shells.

Manufacturing of these carbon-rich products is typically from a hydrocarbon source such as coal or biomass using the steps of pyrolysis (heating in a non-oxidizing environment) and/or further activation (such as reaction with steam at high temperature to increase porosity or surface area). For example, activated carbon with a surface area of 400 m²/g or greater can be produced from lignite coal via the steps of pyrolysis at 450 to 65O⁰C and reacting with steam at temperatures between 750 and 1000⁰C. The production of such carbon-rich solids from parent hydrocarbons results in a hydrogen-rich product gas that is typically not fully utilized in the manufacturing of the carbon-rich solid. For example a very large fraction of the hydrogen-rich product gas in activated carbon production is burnt and then quenched to reduce the flue gas to an adequate temperature for the gas cleaning apparatus, cleaned, and then exhausted into the environment. Such operation is not efficient and results in emission of pollutants including carbon dioxide that are excessive.

In existing activated carbon production plants, a hydrocarbon material like coal or biomass is typically processed through the steps of (i) drying, (ii) carbonization, and (iii) steam activation (contacting with steam at temperatures greater than about 800⁰C to partially gasify the carbonized material and increase its surface activity). These steps can be performed separately, for example, in separate rotary kilns. They can also be performed in one reactor such as a multiple hearth furnace. Instead of steam, carbon dioxide can also be used in the activation step. Both the carbonization and activation steps generate combustible gases. These gases are exhausted from the activation carbon production furnace into a separate combustion chamber where they are oxidized with air to mainly carbon dioxide and water vapor before being sent to an air pollution control system to remove pollutants such as sulfur dioxide and particulate. Steam for the activation step is typically generated in the combustion chamber with a heat exchanger.

Up to 1 pound of steam per pound of feed coal may be required for the activation furnace or about 1000-1200 Btu per pound of feed. This only represents about one-fifth the energy in the combustible gases. In current generation plants, the remainder of the energy is wasted, resulting in a combustible gas energy utilization of only about 20%. For example, the gases are cooled with a water quench before being directed to an air pollution control system. Greater than about 60 percent of the heat in the original starting material for the production of activated carbon is

{Practice Areas\CORP\21311\00005Wt058251.DOC} exhausted into the environment without beneficial use.

Alternatively, in US Patent Application Publication No. 20070254807, an elaborate and expensive steam-to-electricity system is added on to extract some of the energy from the combustible gas into a useful product. The efficiency of conversion to electricity in such plants is only about 25 percent of the energy in the combustible hot gases leaving the activated carbon production process. Also a significant amount of equipment and expense is required to set up the power plant, including steam production heat exchangers (boiler), steam turbines and condensers. A major portion of the heat is exhausted to the environment in the condenser section, where the low pressure steam is contacted with cooling water to condense it before its return to the boiler. The cooling water is then cooled in a cooling tower and heat rejected to the environment before being returned to the condenser. The low energy utilization occurs because only the expansion energy associated with the high temperature, high pressure steam is used in a steam turbine and the latent heat of evaporation associated with the water is rejected to the environment.

SUMMARY OF THE INVENTION

A high efficiency (greater than about 40 percent) and low capital cost solution with effective energy utilization (low carbon dioxide emissions/unit of energy use) is a beneficial means of handling the combustible off-gases from an activated carbon production furnace.

The present invention relates generally to the production of a carbon-rich product (e.g., activated carbon) from a hydrocarbon material such as coal and/or biomass with the generation of excess energy and the generation of a co-product which utilizes about 40% or more of the excess energy for its production. The products that can be co-produced with the carbon-rich product include, but are not limited to, the following: i) Paperboard from wood or recycled paper ii) Wallboard from gypsum iii) Cement clinker from limestone iv) Ethanol from biomass/corn v) Electricity and space heating and cooling.

The combination of the production of the carbon-rich product (e.g. activated carbon), and the production of co-product(s) via energy consuming processes, such as paperboard, gypsum wallboard, cement clinker, ethanol, or space heating, provides significant cost savings through requiring fewer pieces of equipment, reducing material inputs, improving operations and increasing efficiency.

Coal and/or biomass processed for the activated carbon plant produces a hydrogen- enriched combustible gas, which can advantageously be used for process heat in the manufacturing of the co-product, thereby reducing equipment costs, material inputs, and pollutant and greenhouse gas (CO₂) emissions. Activated carbon product resulting from the activated carbon production portion of the inventive process may be used in any activated carbon application including, for example, to reduce heavy metal (e.g. mercury) emissions and/or to control NOx emissions in power plant flue gas, for example, coal-fired power plant flue gas, by contacting the NOx-containing flue gas with activated carbon thereby converting NO to N₂.

One embodiment of the invention produces a carbon-rich product, such as activated carbon, from a hydrocarbon material, such as coal or biomass, while simultaneously utilizing the energy content to greater than about 40 percent efficiency of the hydrogen-rich gases released from the conversion of the hydrocarbon material to a carbon-rich product.

Another embodiment of the invention produces one or more products in addition to the carbon-rich product, these additional products ("co-products") requiring one or more endothermic (energy consuming) steps in their manufacturing process, the energy requirements for which are supplied, at least in part, by the combustion of hydrogen-rich gases released from the conversion of the hydrocarbon material to the carbon-rich product.

Another embodiment of the invention reduces carbon dioxide emissions resulting from the use hydrocarbons, such as coal and biomass, while supplying energy to the endothermic steps in the manufacturing of the co-products.

Another embodiment of the invention minimizes the impact of inorganic constituents (ash) in hydrocarbon fuels, such as coal and biomass, on combustion and heat exchange equipment operation, including ash agglomeration and ash deposition.

Another embodiment of the invention utilizes moisture-rich or carbon dioxide-rich gases released during the manufacturing of the co-products (e.g. in a drying step) as an activating gas in the production of the carbon-rich product from the hydrocarbon material.

Another embodiment of the invention utilizes waste hydrocarbon material generated in the manufacturing of the co-products as a raw material in the reactor for the production of the carbon-rich product. The invention comprises a method and system for co-producing a product (such as gypsum wallboard, paperboard or ethanol) in an energy consuming process and a carbon-rich product (such as activated carbon) from a hydrocarbon material such as coal or biomass.

In this method, carbon-rich product, such as activated carbon, is produced by carbonizing a hydrocarbon material to yield a carbonized product and carbonization product gases; activating the carbonized product with steam or carbon dioxide to yield activated carbon and activation product gases; such that the combination of the carbonization product gases and the activation product gases have a lower carbon-to-hydrogen (C/H) ratio compared to the parent hydrocarbon material. These hydrogen-rich combustible gases are combusted to generate excess energy for use in the manufacture of co-products, which require this input of energy in one or more steps of their production. The use of the hydrogen-rich combustible gas as the energy source minimizes the emission of CO₂ into the environment compared to complete conversion and utilization of the coal or biomass, either through direct combustion or through complete gasification followed by combustion of the gasification products. Also, by only partially converting the carbon content of the parent material, and not releasing the included ash and other inorganic constituents in the carbon material to interact with each other, issues related to deposition on heat transfer surfaces and agglomeration are minimized or eliminated during the energy generation step of combustion of these hydrogen-rich gases. The parent hydrocarbon material can be coal, peat, lignite, bituminous coal, sub-bituminous coal, anthracite, petroleum coke, wood, biomass, or other hydrocarbon waste material such as recycled paper. The parent hydrocarbon material to be used in the invention can also have water associated with it, such as waste paper sludge.

The carbonization and activation product gases (comprising predominantly hydrogen-rich combustible gases) from the carbon-rich product manufacturing process, which have no useful application for any energy consuming steps in the carbon-rich product manufacturing process, are combusted in a burner (or multiple burners) and the sensible and chemical energy in these gases is converted into thermal energy for use in the various steps of the manufacturing of the co-product. This co-product can be, for example, paperboard, gypsum wallboard, ethanol, cement, electricity or space heating.

For example, the hot combustion gases generated in the above step can be used to contact wet materials for drying or for other processes that require heat (endothermic process). Alternatively, or in addition, the hydrogen-rich combustible gases can be directed to a boiler (steam generating unit), where the sensible and chemical energy in the combustible product gases from the activated carbon production is converted by reacting with air (combustion), and the hot gases generated from combustion used to make steam at a temperature and pressure that would be adequate for utilization in the energy consuming steps of co-product manufacturing. Alternatively, or in addition, combustible gases can be directed to a furnace [e.g., heat transfer fluid (oil) heating unit)] where the sensible and chemical energy in the product gases from the activated carbon production is converted to heating a "non-contact heat transfer fluid" that would be adequate for utilization in the energy consuming steps of co-product manufacturing.

In all of the above cases, the flue gas generated from the combustion of activated carbon reactor product gases has a lower CO₂ content per unit of heat generated than direct combustion of the feed coal or biomass.

The inventive method and system of the combined production of carbon-rich high surface area product, such as activated carbon, which generates net excess energy, and a co-product, which requires a net energy input in its manufacturing process is described in several preferred embodiments below.

This invention features a method comprising providing a parent hydrocarbon-rich material, processing the parent material so as to produce both a carbon-rich solid material that has a higher carbon to hydrogen ratio that that of the parent material and a hydrogen-rich combustible gas that has a lower carbon to hydrogen ration than the parent material, the process comprising activating the material by exposing it to a hot gas stream comprising elevated levels of one or both of carbon dioxide and water vapor, combusting the combustible gas to produce heat, and using at least about 40% of the energy content of the combustible gas in a separate process comprising at least one endothermic step. The carbon-rich solid material may be activated carbon with surface area of at least about 200 m²/gm, and more preferably at least about 400 m²/gm.

The endothermic step may include generating electricity. The electricity may be generated by using the heat to produce steam that is used to drive a turbine. The method may further include using the steam leaving the turbine in a heating or drying step in the separate process, thereby using at least about 70% of the energy content of the combustible gas. The electricity may be generated by a gas engine or other device, and the hot exhaust from such a device is used to generate steam that is used in the separate process. The endothermic step may be a step of a separate process selected from the group of separate processes including ethanol production, paperboard production, gypsum wallboard production and cement production. The method may further include adding supplemental fuel to the combustible gas before the combusting step, to more closely meet the thermal needs of the separate process. The endothermic step may involve water evaporation or drying, material heating, or calcinations. The method may further include using the heat produced from combustion in a separate process comprising at least one endothermic step, the separate process resulting in part in a gas stream comprising elevated levels of one or both of carbon dioxide and water vapor, and then using the gas stream at least in part as either the hot gas stream for activation of the carbon-rich solid material, or to cool the carbon-rich solid material.

The separate process may include ethanol production. The heat from combustion may be used to generate steam that is used in one or more endothermic steps of the ethanol production. The method may further include adding supplemental fuel to the combustible gas before the combusting step. The ethanol production may result in the emission of volatile organic compounds (VOCs), wherein the at least some of the VOCs are used as a supplemental fuel. The ethanol production may result in the emission of volatile organic compounds (VOCs), wherein the at least some of the VOCs are combusted to produce heat used in the step of processing the parent material so as to produce both a carbon-rich solid material that has a higher carbon to hydrogen ratio that that of the parent material and a hydrogen-rich combustible gas that has a lower carbon to hydrogen ration than the parent material.

The separate process may include paperboard production. The heat of combustion may be used to generate hot gas or steam that is used to dry the paperboard. The method may include adding supplemental fuel to the combustible gas before the combusting step, to generate sufficient steam for paperboard production. The parent material may include cellulosic waste from the paperboard production.

The separate process may include gypsum wallboard production. The method may further include adding supplemental fuel to the combustible gas before the combusting step.

The separate process may include cement production. The method may include adding supplemental fuel to the combustible gas before the combusting step.

The invention also features a method comprising providing a parent hydrocarbon-rich material, processing the parent material so as to produce both a carbon-rich solid material that has a higher carbon to hydrogen ratio than that of the parent material and a hydrogen-rich combustible gas that has a lower carbon to hydrogen ration than the parent material, the process comprising activating the material by exposing it to a hot gas stream comprising elevated levels of one or both of carbon dioxide and water vapor, combusting the combustible gas to produce heat, using the heat produced from combustion in a separate process comprising at least one endothermic step, the separate process resulting in part in a gas stream comprising elevated levels of one or both of carbon dioxide and water vapor, and using the gas stream at least in part as either the hot gas stream for activation of the carbon-rich solid material, or to cool the carbon- rich solid material.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other features and advantages of the present invention will become fully appreciated as the invention becomes better understood when considered in conjunction with the accompanying drawings, in which:

Figure l is a schematic flow diagram of an integrated activated carbon and ethanol production plant according to the invention;

Figure 2 is a schematic flow diagram of an integrated activated carbon and paperboard production plant according to the invention;

Figure 3 is a schematic flow diagram of an integrated activated carbon and paperboard production plant with waste paper utilization according to the invention;

Figure 4 is a schematic flow diagram of an integrated activated carbon and gypsum wallboard production plant according to the invention;

Figure 5 is a schematic flow diagram of an integrated activated carbon and gypsum wallboard production plant that uses energy for gypsum drying according to the invention;

Figure 6 is a schematic flow diagram of an integrated activated carbon and gypsum wallboard production plant that uses energy for gypsum calcination according to the invention; and

Figure 7 is a schematic flow diagram of an integrated activated carbon and cement production plant according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

This invention may be accomplished in a method and system for co-producing a product (such as gypsum wallboard, paperboard or ethanol) in an energy consuming process and a carbon-rich product (such as activated carbon) from a hydrocarbon material such as coal or biomass. This is performed by directing the hydrogen-rich combustible gases from the activated carbon production reactor and using its energy content by combusting it and using the released energy to a high efficiency in the energy consuming steps of manufacturing of the co-product.

The preferred embodiments are described below. I. Activated Carbon and Ethanol Co-production

• Activated carbon production from hydrocarbon feedstock and production of lower C/H ratio hot combustible product gas than parent feedstock

In this method (Figure 1) activated carbon and ethanol are produced in co-production plant (10). Activated carbon is produced in the activated carbon manufacturing plant section (20) by carbonizing a solid or partially solid (e.g. wet) carbonaceous material to yield a carbonized product and carbonization product gases; activating the carbonized product with steam or carbon dioxide to yield activated carbon and activation product gases; such that the combination of the carbonization product gases and the activation product gases (hydrogen-rich hot combustible product gases from the activated carbon reactor) have a lower carbon-to-hydrogen (C/H) ratio compared to the parent carbonaceous material. In the above method carbonizing or pyrolysis is typically performed at 400 to 600⁰C and activation with steam is performed at 700 to 1000⁰C.

Activated carbon produced by the above method has a surface area of at least 200 m²/gm, preferably at least, 350 m /gm, and more preferably at least 500 m /gm. Surface areas are determined by the Brunauer-Emmett-Teller N₂ adsorption method.

A multiple hearth furnace (MHF) may be used as the activated carbon production reactor (26). Coal or other carbonaceous feedstock is prepared via hammer mills (24) to about 1/8" to ¹Z." in size and introduced to the top of the activated carbon production reactor. The carbonaceous material goes through a series of steps including drying, devolatilization and activation in the MHF to product activated carbon. The hot gases leaving the activated carbon production reactor contain fine particulate. The fine particulate, which is partially processed material, is collected in a cyclone (28) and advantageously returned to the reactor for further processing.

Chemical activation of the carbonaceous feedstock instead of physical activation may also be used. In chemical activation, the carbonaceous material is mixed with a dehydrating agent such as zinc chloride, phosphoric acid or alkali hydroxide such as potassium hydroxide. This is followed by heat treatment to temperatures between 450 and 900⁰C to carbonize the material and release hot combustible product gases.

In this first embodiment, the co-product manufactured through one or more energy consuming steps is ethanol. In the ethanol manufacturing section (50) of the process (Figure 1), corn or other high-starch grains (or other biomass used in ethanol production) is first ground into meal and then slurried with water to form a mash. Enzymes are added to the mash to convert the starch to the simple sugar, dextrose. Ammonia is also added for pH control and as a nutrient to the yeast. The mash is processed in a reactor (52) through a high temperature cook step, which reduces bacteria levels prior to fermentation. Steam is used for the high temperature cooking step.

The mash is then cooled and transferred to fermentation vessels where yeast is added and the conversion of sugar to ethanol and carbon dioxide (CO₂) begins.

After fermentation, the resulting "beer" is transferred to distillation where the ethanol is separated from the residual "stillage". The ethanol is concentrated to 190 "proof using conventional distillation in the distillation column (54). Steam is used for the distillation step.

The residual "stillage" from distillation is separated into a coarse grain fraction and a "soluble" fraction by centrifugation in the centrifuge (56). The soluble fraction is concentrated to about 30% solids by evaporation in the evaporator (58). This intermediate is called Condensed Distillers Solubles (CDS) or "syrup." Steam is used for the evaporation process.

The coarse grain and syrup fractions are then mixed and dried to produce distillers dried grain and solubles (DDGS), a high protein animal feed product in the dryer (60). Steam is used for drying step.

As described above, the production of ethanol from corn requires energy, in the form of steam, for various processing steps - about 10% in the cooking process, 30% in the ethanol evaporation, 15% in ethanol distillation and 45% for drying the distiller grains. About 35,000- 40,000 Btu of process heat per gallon of ethanol is required. For example, a 50 million gallon per year ethanol production plant will use about 1,540 million pounds of steam per year (steam at 365⁰F, 150 psig). This translates to about 180,000 lbs/hr of steam.

Ethanol may be manufactured by other energy consuming methods such as hydrolysis or gasification and with starting materials such as cellulose. These processes also require energy in their various transformation steps, and this invention covers these methods as well. • Production of steam for the ethanol manufacturing plant from the combustion of hot combustible product gas from the activated carbon production plant

In this embodiment of the inventive process, activated carbon and ethanol are co- produced in a plant (Figure 1), and at least a portion of the steam (process heat) required for the ethanol section of the plant is produced through the combustion of hydrogen-rich combustible gas generated in the activated carbon production reactor. The combustor/boiler (32) is one known in the art and typically comprises a burner, combustion chamber and heat transfer coils. The heat generated from the combustion process is transferred to water entering the heat transfer coils. Water is converted to a pressurized and hot steam flow that can be advantageously used in the various endothermic steps of ethanol manufacturing.

• Cooling of hot activated carbon product with COr-rich or moisture-rich gases from ethanol plant

Activated carbon leaving the bottom of the activated carbon production reactor, such as a MHF is at a high temperature, typically around 1500 to 1700⁰F. This hot material is typically cooled with an indirect heat exchanger before being discharged. In an embodiment of the invention, the hot activated carbon product is advantageously cooled with moisture-rich gas stream or Cθ₂-rich gas stream from the ethanol plant in a heat exchanger (not shown). The heat exchanger can be of an indirect contact type, or a direct contact heat exchanger. If direct contact heat exchange is used, the gas streams should have a maximum of about 1 percent O₂, preferably less than 0.5% O₂ to prevent oxidation and degradation of the activated carbon product. The heat exchanger is preferably operated in a predominantly counter-current mode, with the hot activated carbon product and the "cooling" gas streams flowing in a counter-current fashion. The heated (moisture-rich or CO₂-rich) gas stream can then be advantageously used subsequently as process gas in the activation step of the activated carbon plant.

• Use of moisture-rich or CO^-rich exhaust gases from the ethanol manufacturing plant as process feed gas for activation in the activated carbon production reactor

In another embodiment of the combined activated carbon and ethanol plant, at least a portion of several exhaust gas streams in the ethanol manufacturing section plant that are almost pure steam (moisture) or CO₂ are used as activation process gas. For example, if an indirect steam-driven dryer is used for the production of DDGS, the exhaust gases from the dryer (from the drying process) are almost completely pure water vapor. The gases leaving the fermentation section of the ethanol manufacturing section of the plant are almost completely pure CO₂. These streams may be advantageously used as process gas for the activation step in the activated carbon plant. These gas streams may be advantageously preheated as described in the preceding paragraphs before introduction into the activation section of the activated carbon plant. By using the moisture-rich stream from the ethanol plant in the activated carbon plant, water and energy consumption for the combined plant is reduced, since steam required for the activation step in the activated carbon plant does not have be raised separately.

The flue gas from the combustion of the hydrogen-rich combustible gas produced by the activated carbon reactor is treated to reduce the concentration of various pollutants in a manner that is known in the art. For example, ammonia can be injected in the flue gases at a temperature of about 1500-1800⁰F to reduce the nitrogen oxides to molecular nitrogen. Alkaline material, such as lime slurry can be injected into the flue gas to capture sulfur oxides, and the coal ash and scrubber particulate can be removed using a dust collector such as a fabric filter.

• Co-firing of coal and hot combustible product gas from the activated carbon production plant for steam production for ethanol manufacturing

In an alternate embodiment, if the ethanol section of the plant requires more energy than what is provided by the combustion of the hydrogen-rich combustible gas from the activated carbon reactor, supplemental firing of additional fuel may be used. This additional fuel can be coal, preferably, or an alternate fuel, such as natural gas.

The hydrogen-rich combustible gas from the activated carbon production reactor may be fired simultaneously with the supplemental fuel in an advantageous manner to reduce pollutant emissions such nitrogen oxides. For example, the hydrogen-rich combustible gas may be preferentially introduced in a reducing zone of the combustor, followed by staged addition of combustion air into the combustor to minimize nitrogen oxide formation and complete combustion. Alternately, the combustible product gas can be introduced into the combustor as a "re-burn" fuel at a downstream location of the combustor to reduce nitrogen oxides formed upstream in the combustor.

• Boosting pressure of the hot combustible product gas from the activated carbon plant Depending on the operation of the activated carbon reactor, the hydrogen-rich combustible gas from the reactor may need to be delivered at a higher pressure to downstream components/devices than made available at the exit of the reactor. A higher pressure may be required, for example, to obtain better distribution of the combustible gas within a downstream device. In such cases, a fan (30) that can handle hot and parti culate-laden gas streams may be used. If the combustible gas from the activated carbon plant has too high a temperature for it to be effectively handled by a fan, then it may be cooled down to the necessary temperature before its introduction into the fan. Cooling may be achieved with a heat exchanger, where additional steam can be generated, or by mixing in a cold gas stream.

• Handling of water/steam from and to the boiler/combustor

The boiler/combustor (32) that burns the combustible gas from the activated carbon reactor has a water inlet and steam outlet. Boiler feed water is compressed to a desired pressure and pumped through the boiler tubes and extracts heat from the hot gases generated from the combustion of the combustible product gas with air. Steam temperature and pressures are chosen to efficiently operate and satisfy the heat demand of the various ethanol manufacturing steps. Typical conditions for steam supply to the ethanol plant are 150 psig pressure and 37O⁰F temperature.

In some of the production steps in the ethanol plant, steam is contacted directly with other materials. In other production steps such as the drying and production of the DDGS, steam is used in an indirect manner and does not contact other materials. In such cases, the condensed steam (after its useful energy has been transferred) is redirected to the boiler as boiler feed water. Additional (make-up) boiler feed water from a boiler feed water treatment plant is mixed with the returning condensate and then sent to the combustor/boiler.

• Destruction of volatile organic compounds in exhaust streams from ethanol manufacturing in the activated carbon production plant or the combustor/boiler Ethanol manufacturing uses various process steps and pieces of equipment that emit volatile organic compounds (VOC). VOCs may be emitted from the dryer, distillation columns, thermal oxidizer units, wet cake storage locations, fermentation tanks, and other equipment associated with fermentation and distillation such as fluid bed coolers, cooling cyclones (62), and fermentation scrubbers. To prevent emission of VOC into the environment, these streams may be advantageously routed to the combustor/boiler (32). If these streams are oxygen-rich (i.e. predominantly air), they may be advantageously used as combustion air for the combustor/boiler. In this manner, the high temperatures and oxidizing environment in the combustor/boiler can effectively destroy the VOC. To improve heat/process efficiency, these streams may be heat exchanged with the exhaust streams from the combustor/boiler (combustion air pre-heat), prior to being used as combustion air in the combustor/boiler.

The VOC-laden air streams from the ethanol plant can also be used as process air and burner air in the activated carbon production reactor (26), although these quantities are expected to be much smaller than that required for the combustor/boiler.

The fermentation reactor in the ethanol manufacturing plant produces a CO₂-rich stream. This stream also has VOCs, which are typically removed with a dedicated scrubber. In this embodiment of the inventive co-production plant, the CO₂-rich stream with minor quantities of VOC can be advantageously directed to the activation section of the activated carbon plant and used as activation gas similar to steam. In this manner, a scrubber for the fermentation reactor may be avoided or used only when the activated carbon plant is not operating.

Examples

Example 1 - Ethanol and Activated Carbon Production Plant

An ethanol and activated carbon production plant with the identified improvements

(Figure 1) and advantages relative to stand-alone plants is described below.

Coal (lignite) of the composition provided below is used as feed stock.

Composition wt-%

C Carbon 34.6

H Hydrogen 3.5

S Sulfur 0.61

O Oxygen 21.6

N Nitrogen 0.66

Ash 7.0

H₂O Moisture 32.0

Activated carbon yield from the activated carbon production reactor is about 20-30 percent based on wet feed input. For a 46,684 lb/hour wet lignite input, this plant yields about 9,580 lb/hour (20% yield) of activated carbon product.

A typical activated carbon composition is shown below obtained from processing the above-described feed stock in the proposed inventive method.

Composition wt-%

C Carbon 68

H Hydrogen 0.5

S Sulfur 1.5

O Oxygen 0.5

N Nitrogen 0.7

Ash 28.0

H₂O Moisture 1.0

Steam requirement for activation for the activated carbon production plant is about 0.7 Ib of steam per pound of wet feed. For a 46,684 lb/hour wet lignite input, this translates to about 32,680 lb/hour of steam. This quantity of moisture-rich gas is almost completely available from the ethanol DDGS dryer. For example, in the case shown the production amount of DDGS is 22 tons per hour, the corresponding amount of associated moisture would have been approximately 15 tons per hour or 33,000 lbs/hour of water vapor. If additional steam is required, some of the steam generated in the combustor/boiler can be directed to the activation zone of the activated carbon production reactor. In the example discussed here, since the water vapor requirement for the activation step is met almost completely by the dryer exhaust gases of the ethanol plant, no additional fuel firing is required to generate this steam, unlike in a traditional activated carbon production plant.

The carbonization and activation product gases (comprised predominantly of combustible gases) from the activated carbon production reactor are combusted in a boiler (steam generating unit) where the sensible and chemical energy in the activated carbon reactor product gases is converted to making steam at a temperature and pressure that is adequate for utilization in an ethanol plant. The boiler as described above comprises a combustion zone, where activated carbon reactor gases are combusted with air. To completely combust the hot combustible product gas from the activated carbon production reactor, in this example, about 142,670 lb/hour of combustion air is required (corresponding to an excess air of about 20 percent). This air stream is supplied from the various exhaust streams of the ethanol plant, which are predominantly composed of air with trace quantities of VOC. In this manner, a separate VOC destruction device is not required for the ethanol plant.

The steam produced (163,250 lb/hour) in the boiler from the combustion of the hot combustible product gases from the activated carbon reactor is advantageously directed to a corn-to-ethanol plant, where the steam is used as the energy source for various ethanol- manufacturing process steps, including process heat, ethanol distillation, evaporation and concentration of raw stillage, and drying of residual wet solids to dry distillers' grain solids (DDGS).

Alternatively, the steam produced in the boiler from the combustion of the hydrogen-rich combustible gases may also be directed to a power (back pressure) turbine to generate electricity, and exhaust steam from the turbine directed to the corn-to-ethanol plant section for process heat, including, for example, ethanol distillation and evaporation. In this case, the excess energy from the activated carbon production is used for both electricity production and process heat. Electricity may also be produced from the combustible gases directly in a gas engine and the hot exhaust of the gas engine advantageously directed to generate steam for the endothermic steps in the co-product (ethanol) manufacturing.

The flue gas generated from the combustion of activated carbon reactor product gases has a lower CO₂ content per unit of heat generated than direct combustion of the feed coal or biomass. For example, in the above example 35,510 lbs/hour of CO₂ is generated for the required amount of steam for the ethanol plant operations, compared to 40,700 lbs/hour of CO₂ with direct coal combustion in an ethanol plant (see comparative example below).

The energy content in the coal used is about 6400 Btu/lb and the total energy content coming into the process with the coal is 298 MMBtu/hr. The energy content leaving the process with the activated carbon is about 96 MMBtu/hr. The remainder, excluding heat loss to the environment, is about 200 MMBtu/hr and is the energy content of the hydrogen-rich combustible gases. The energy used to evaporate the steam (163,250 lb/hr) is about 170 MMBtu/hr. The efficiency of energy utilization is about 85 percent.

The total amount of coal used for a integrated ethanol and activated carbon plant is 46,684 lb/hour to produce 163,250 lb/hour of steam (required for 5820 gallon per hour ethanol manufacturing plant) and 9580 lb/hour of activated carbon product. In comparison, a separately located coal-fired ethanol plant and a coal-fed activated carbon plant with flue gas quench would require a total of 78,180 lb/hour of coal. The total CO₂ emissions from separately located plants would be 76,210 Ib of CO₂/hour compared to 35,510 Ib of CO₂/hour for an integrated plant. Even if the separate activated carbon production plant is equipped with recovering the excess heat and converting it to electricity, the efficiency of conversion is only about 20 to 25 percent compared to above about 80 percent for the integrated ethanol-activated carbon plant.

Comparative Examples

Example 2 - Separate Coal-Fired Boiler for Ethanol Manufacturing:

A typical coal-fired boiler necessary for making steam to supply a 50 million pound per year plant (5820 gallons of ethanol per hour) is estimated to be about 163,250 lb/hr of steam. Steam conditions are 150 psig and 365⁰F. About 32,100 lb/hour of coal firing is required to generate the above steam quantity. The coal considered in this case is a lignite coal as described in the example with the integrated plant. Such a boiler would need to be equipped with heat extraction in the combustion section to keep flue gas temperatures at an operationally acceptable level, if low quantities of excess air (< 20 percent) are to be used.

Combustion of the above indicated quantity of coal will generate about 186,380 lb/hour of flue gas, if the excess air used is about 20 percent above the stoichiometric requirement. Corresponding quantity of CO₂ emissions in the flue gas is about 40,700 lbs/hour.

Alternatively, if a combustor without heat extraction in the combustion zone is to be employed, flue gas temperatures would need to be moderated typically by cooling with high amounts of excess air (~ 300 percent). An example of this case would be to use 518,230 lb/hr of air with 36,439 lbs/hour of coal to generate 555,000 lbs/hr of flue gas and 46,197 lbs/hr of CO₂ and still only generate the above-identified quantity and quality of steam (163,250 lb/hr, 150 psig and 365⁰F)

Example 3 - Coal-Fired Activated Carbon Plant with Flue Gas Quench:

An example of a typical coal-fired activated carbon production plant is provided below. Lignite of the composition provided in the previous example is used as feed stock. Activated carbon yield is about 20 percent based on wet feed input. A portion of the heat generated from the combustion of the product gases from the reactor is used to generate process steam. Steam requirement for the activated carbon production plant is about 0.7 Ib of steam per pound of wet feed. For a 46,684 lb/hour wet lignite input, this translates to about 32,680 lb/hour of steam. This plant yields about 9,580 lb/hour of activated carbon product. The remainder of the heat from the combustion of the product gas from the activated carbon production reactor has to be quenched with a water spray. About 133,380 lb/hour of water is required to quench the flue gases and achieve an outlet flue gas temperature of about 300⁰F, which is optimum for operation of the pollution control equipment. This process yields an overall flue gas flow of 344,940 lb/hour (20 percent excess air) and CO₂ emission of about 35,510 lb/hour, but the energy in the hydrogen- rich combustible gases is not utilized.

Example 4 - Coal-Fired Activated Carbon Plant with Heat Recovery for Power Generation:

In a typical coal-fired activated carbon production plant flow diagram with heat recovery for power generation, lignite of the composition provided in the previous examples is used as feed stock. Activated carbon yield is about 20 percent based on wet feed input. A portion of the heat generated from the combustion of the product gases from the reactor is used to generate process steam. Steam requirement for the activated carbon production plant is about 0.7 Ib of steam per pound of wet feed. For a 46,684 lb/hour wet lignite input, this translates to about 32,680 lb/hour of steam. This plant yields about 9,580 lb/hour of activated carbon product. The remainder of the heat from the combustion of the product gas from the activated carbon production reactor is cooled, while additional steam is generated. This steam is sent to a steam turbine for electricity production. About 10 MWe of electricity can be expected to be produced, with a heat-to-electricity conversion of about 20-25%. This process yields an overall flue gas flow of 212,380 lb/hour (20 percent excess air) and CO₂ emission of about 35,510 lb/hour.

Electricity generation using a steam turbine by itself, typically only has energy efficiency utilization between 20 and 35 percent, but for a plant of this size closer to 20 to 25 percent. The remainder of the energy is lost to the environment during steam condensation in the condenser, which is necessary to return water into a liquid state before it can be compressed and returned to the boiler. II. Activated Carbon and Paperboard Co-production

In another preferred embodiment, (Figure 2) activated carbon is produced in the activated carbon manufacturing plant section (20) of the activated carbon and paperboard co-production plant (80) from the starting hydrocarbon material such as coal or biomass in a similar fashion as outlined in previous embodiments and the co-product manufactured through one or more energy consuming steps is paperboard. Energy for various endothermic steps of paperboard production is supplied from the excess energy that is generated from activated carbon production and which is associated with the hydrogen-rich combustible gases generated therein.

Figure 2 is one embodiment of the present disclosure of a system for an integrated activated carbon and paperboard production process. Figure 3 is another embodiment of the present disclosure of a system for an integrated activated carbon and paperboard production process with waste paper utilization.

To form paperboard in the paperboard manufacturing section (90), recycled fiber mixed with water and other additives is discharged into a forming line. The "wet" board is then moved to dryer lines (92) where excess moisture is evaporated in a controlled manner. Energy for board drying is supplied by steam. Typically, a drum or a surface heated with steam is contacted with the wet paper for the drying operation. Alternately, an air stream may be heated by the steam via a heat exchanger and the heated air stream supplied to the dryer to evaporate the water.

Typically energy requirement for paperboard production is about 4-8 MMBtu/ ton.

• Production of process heat for paperboard manufacturing plant from the combustion of hot combustible product gas from the activated carbon production plant

In this embodiment, hot combustible gases generated from the pyrolysis and steam gasification of the solid or partially solid carbonaceous material such as coal, carbonaceous waste from the paperboard plant, or other biomass is combusted with air in a boiler (32) to generate at least some portion of the process heat/steam for the paperboard manufacturing section of the plant. By using a potentially wasted fuel, the energy costs for the paperboard manufacturing are minimized and efficiency maximized.

In the paperboard making process, a significant amount of wet cellulosic waste is generated during the initial screening process.

• Utilization of carbonaceous residues/waste from the paperboard plant in the activated carbon production plant to produce activated carbon and process heat/process steam In this embodiment (Figure 3), the carbonaceous residues/waste from the paperboard making steps can be advantageously fed to the activated carbon manufacturing section (20a) at the top of the activated carbon multiple hearth furnace (front of the activated carbon manufacturing process) along side other carbonaceous feed materials to produce activated carbon and hot combustible product gases. Separate or dedicated equipment is not required for processing the residue/waste stream. Since the carbonaceous materials from the paperboard plant are renewable (biomass-derived), the combustible gases generated from the pyrolysis and activation of the said material, their combustion and subsequent heat extraction and utilization will result in less carbon dioxide emissions resulting from the combustion of fossil-derived fuels. The paperboard is co-produced in the paperboard manufacturing section of the plant (90a).

The emissions of pollutants including carbon dioxide can be significantly reduced with the above invention because of the utilization of the waste energy from the carbon manufacturing section of the plant in paperboard manufacturing as well the use of waste carbonaceous ("renewable") materials in the paperboard section of the plant in the activated carbon manufacturing.

• Co-firing of natural gas and hot combustible product gas from the activated carbon production plant for process heat for paperboard manufacturing

In an alternate embodiment, if the paperboard plant has larger heat requirements than what can be provided by the hydrogen-rich gas from the activated carbon reactor, then supplemental fuel, such as natural gas, may be advantageously co-fired or fired separately in the boiler.

• Controlling temperature of the gases for process heat for paperboard manufacturing The temperature required for the drying and other operations may be limited by process considerations. Temperature of the hot product gases generated from the combustion of the hydrogen-rich combustible gases from the activated carbon reactor may be controlled by mixing "cold" recycled flue gas in a proportion to achieve the desired temperature values.

• Process control for paperboard manufacturing

In another embodiment, natural gas is used in combination with the combustible product gases from the activated carbon production reactor to enable control of the steam generated for paperboard production. The proportion of natural gas can be minimized and set at values just necessary for process control. Control of the quantity of steam as defined by the requirements of the paperboard plant, is achieved by monitoring the steam quantities generated from the combustible gases from the activated carbon production reactor and supplementing it with natural gas or oil firing. Process control is achieved by varying the amount of natural gas or oil firing and steam generation associated with that firing.

Co-firing of natural gas and activated combustible product gas from the activated carbon production reactor also enables "assured" process operation or back-up fuel in case natural gas supply is interrupted or the activated carbon production reactor has to be shut down.

Similar to the previous embodiment in the co-production of activated carbon and ethanol, the following advantageous aspects are included in the preferred embodiments of co-production of activated carbon and paperboard.

(i) Cooling of hot activated carbon product with moisture-rich gases from paperboard manufacturing.

(ii) Use of moisture-rich exhaust gases from the paperboard manufacturing as process feed gas for carbon activation in the activated carbon production reactor

Examples

Example 5 - Integrated Paperboard and Activated Carbon Production Plant

An integrated paperboard and activated carbon production plant with the identified improvements (Figure 2) and advantages relative to stand-alone plants is described below.

Lignite of the composition provided below is used as feed stock.

Composition wt-%

C Carbon 34.6

H Hydrogen 3.5

S Sulfur 0.61

O Oxygen 21.6

N Nitrogen 0.66

Ash 7.0

H₂O Moisture 32.0

The production of process heat for the paperboard production process is described below. About 23,340 lb/hour of coal is introduced into a multiple hearth furnace. About 71,400 lb/hour air and 16,340 lb/hour steam is introduced in the various hearths of the MHF and hot product gas combustor to generate the heat required and provide the optimum gaseous environment for the production of activated carbon as well as combust all hydrocarbon and other combustible gases from the activated carbon production reactor. About 4,790 lb/hour of activated carbon is produced from this reactor set-up. The hot combustible product gases leaving the multiple hearth furnace (activated carbon production reactor - ACPR) at the top is sent to a combustor/steam boiler. Air is added to the burner to completely combust the hydrocarbons to yield hot flue gas, which transfers its heat via a heat exchanger to make product steam (81,630 lb/hour, 37O⁰F). This steam is sent to the paperboard plant and used for paper drying and other process heating purposes. In the paperboard plant, the steam is condensed, transferring its heat mostly completely to the paper-making process. The loss of heat to the environment is mainly through equipment walls and in the flue gas (clean exhaust) leaving the system.

Overall heat utilization efficiency of greater than 70 percent and more preferably 80 percent of the chemical and sensible heat in the hot combustible product gas from the activation carbon production reactor to boiler is achieved. The condensate obtained from steam condensation in the papermaking process is returned to the boiler to be heated and evaporated again.

In the above set-up, about 17,760 Ib of CO₂ is generated from coal and 81,630 Ib. of steam (at 37O⁰F) is generated via heat extraction resulting in 0.218 Ib CO₂ per pound of steam generated. CO₂ emission for each pound of steam generated by this method where activated carbon is produced and the remainder (consisting of hydrogen-rich combustible gases) is used for steam production (or heat utilization) is about 12.5 percent lower than the comparative example of direct combustion of coal or combustion followed by complete gasification of coal, where all of the carbon content in the fuel is used for heating.

The energy content in the coal used is about 6400 Btu/lb and the total energy content coming into the process with the coal is 150 MMBtu/hr. The energy content leaving the process with the activated carbon is about 49 MMBtu/hr. The remainder, excluding heat loss to the environment, is about 100 MMBtu/hr and is the energy content of the hydrogen-rich combustible gases. The energy used to evaporate the steam (81,630 lb/hr) is about 85 MMBtu/hr. The efficiency of energy utilization is 85 percent.

Example 6 - Integrated Paperboard and Activated Carbon Production Plant with Waste Paper Utilization

An integrated paperboard and activated carbon production plant with the identified improvements with waste paper utilization (Figure 3) and advantages relative to stand-alone plants is described below. Waste paperboard of the composition provided below is used as feed stock. Composition wt-%

C Carbon 26.0

H Hydrogen 3.5

O Oxygen 26.4

Ash 4.0

H₂O Moisture 40.0

Lignite of the composition provided below is also used as feed stock.

Composition wt-%

C Carbon 34.6

H Hydrogen 3.5

S Sulfur 0.61

O Oxygen 21.6

N Nitrogen 0.66

Ash 7.0

H₂O Moisture 32.0

The production of process heat for the paperboard production process and utilization of the waste paper sludge in the activated carbon production process is described below. About 23,340 lb/hour of coal is introduced into a multiple hearth furnace. About 6,600 lb/hour of waste paper sludge (40% moisture) is also introduced to the top of the multiple hearth furnace. About 91,000 lb/hour air and 18,320 lb/hour steam are introduced in the various hearths of the MHF and hot product gas combustor to generate the heat required and provide the optimum gaseous environment for the production of activated carbon as well as combust all hydrocarbon and other combustible gases from the activated carbon production reactor. About 5,100 lb/hour of activated carbon is produced from this reactor set-up. The yield of activated carbon based on the feed coal is approximately 20 percent. The yield of activated carbon based on the feed paper waste is approximately 5 percent. The hot combustible product gases leaving the multiple hearth furnace (activated carbon production reactor) at the top is sent to a combustor/steam boiler. Air is added to the burner to completely combust the hydrocarbons to yield hot flue gas, which transfers its heat via a heat exchanger to make product steam (106,25 Olb/hour at 375⁰F). This steam is sent to the paperboard plant and used for paper drying and other process heating purposes. In the paperboard plant, the steam is condensed transferring its heat almost completely to the paper- making process. The condensate is returned to the boiler to be heated and evaporated again.

In the above set-up, about 17,760 Ib of CO₂ is generated from coal (no increase compared to Example 5, since a renewable source, i.e. waste paperboard, is used) and 106,250 Ib of steam are generated resulting in 0.167 Ib CO₂ from coal per pound of steam generated. CO₂ emission for each pound of steam generated by this method where a renewable source such as waste paper is used for a portion of the feed, activated carbon is produced, and the remainder (consisting of hydrogen-rich combustible gases) is used for steam production (or heat utilization) is about 33 percent lower than the comparative example of direct combustion of coal or combustion followed by complete gasification of coal, where all of the carbon content of the fuel is used for heating.

The energy content in the coal used is about 6400 Btu/lb and the total energy content coming into the process with the coal is 150 MMBtu/hr. The energy content of the waste paper is about 37 MMBtu/hr. The energy content leaving the process with the activated carbon is about 52 MMBtu/hr. The remainder, excluding heat loss to the environment, is about 135 MMBtu/hr and is the energy content of the hydrogen-rich combustible gases. The energy used to evaporate the steam (106,245 lb/hr) is about 110 MMBtu/hr. The efficiency of energy utilization is about 82 percent. III. Activated Carbon and Wallboard Co-production

In another preferred embodiment, (Figure 4) activated carbon and wallboard are co- produced in a plant (100). Activated carbon is produced from the starting hydrocarbon material such as coal or biomass in a similar fashion as outlined in previous embodiments and the co- product manufactured through one or more energy consuming steps is gypsum wallboard. Energy for various endothermic steps of wallboard production is supplied from the excess energy that is generated from activated carbon production and which is associated with the hydrogen- rich combustible gases generated therein.

Figure 4 is one embodiment of the present disclosure of a system for an integrated activated carbon and wallboard production process plant. Figures 5 and 6 are detailed examples of this embodiment identifying the energy sharing between the activated carbon production reactor and the gypsum drying and gypsum calcination steps of wallboard production.

In the wallboard manufacturing process, raw gypsum (synthetic or mined) is first dried, for example in a cage mill, using hot process gas typically obtained from natural gas firing. The dried gypsum (land plaster) is then calcined to form Plaster of Paris (CaSO₄-¹AH₂O) or stucco. The temperature of calcination is around 300 to 35O⁰F. Calcination is performed in an impact mill, where hot gases, typically produced from the combustion of natural gas, are contacted with the gypsum. Both size reduction and calcination are performed simultaneously to yield a fine calcined powder. Alternately, calcination can be performed in a kettle calciner, where the heat is transferred to the gypsum particles indirectly. To form the wallboard, the stucco is then mixed with water and other additives and discharged into a forming line. A portion of the water added to the slurry is consumed in formation and re-crystallization of gypsum in the wallboard. The "wet" board is then moved to dryer lines where the excess moisture is evaporated in a controlled manner.

As described above, wallboard production requires heat for various processing steps - up to 20% in the feed gypsum drying, another 25% in gypsum calcination, and about 55% in board drying. About 2 MMBtu/ MSF (MSF = 1000ft²) of wallboard is required for the overall production.

• Production of process heat for wallboard manufacturing plant section Tl 10) from the combustion of hot combustible product gas from the activated carbon production plant

In this combined activated carbon and wallboard co-production process (Figure 4), at least a portion of the process heat required for the wallboard production is generated through the combustion of hydrogen-rich combustible product gas that is generated in the activated carbon production reactor.

In one embodiment, a portion of the hot combustible product gas from the activated carbon production reactor is directed to the burner (112) of the raw feed dryer. Combustion air is added to the burner to burn the fuel gases and generate a hot combusted product gas that can be contacted directly with the wet feed to evaporate the water and dry the gypsum material. The contacting of the hot gases and the wet gypsum can also be performed in a rotary kiln dryer (120) or any other type of drying equipment. To modulate the temperature of the hot gases contacting the wet gypsum, a recycle fan (126) may be used to re-circulate cold exhaust gases from the dryer (120a) exit to the front of the dryer or the burner (112d) as shown in Figure 5.

In addition to the above, another portion of the hot combustible product gas from the activated carbon production reactor can be directed to the burner (112a) of the gypsum calciner (122) (Figure 4). Combustion air is added to the burner to burn the fuel gases and generate a hot combusted product gas that can be contacted directly with the gypsum feed to calcine the gypsum and drive off the chemically bound water and form stucco. The contacting of the hot gases and the gypsum can be performed in an impact mill, where both calcination and grinding is performed. Alternately the hot gases can be used to transfer the heat to the gypsum in a kettle calciner where the heat is transferred to the gypsum in an indirect manner.

To modulate the temperature of the hot gases contacting the gypsum in the calciner, a recycle fan (126a) may be used to re-circulate cold exhaust gases from the calciner (122a) exit to the front of the calciner or the burner (112e) as shown in Figure 6.

In addition to the above, another portion of the hot combustible product gas from the activated carbon production reactor can be directed to a boiler (112c) or hot oil heater (112b) and combusted to generate hot combusted gas (Figure 4). In either of these devices, steam or "hot" oil is produced by transferring the heat from the combustion gases to process fluid. The "hot" steam and/or "hot" oil is directed to the board dryer (124), where the heat transferred to gases that are used to dry the wallboard. The steam and/or the "hot oil" act as a heat transfer fluid. In this manner, a clean gas stream can be used to dry the wallboard and contact with the "dirty" gases from the combustion of the hot combustible product gas from the activated carbon production reactor is prevented.

• Process control for wallboard manufacturing

In another embodiment, natural gas is used in combination with the combustible product gases from the activated carbon production reactor to enable control of the temperature of the hot gas mixture. The proportion of natural gas can be minimized and set at values just necessary for process control.

Co-firing of natural gas and activated combustible product gas from the activated carbon production reactor also enables "assured" process operation or back-up fuel in case the activated carbon production reactor (ACPR) has to be shut down.

Several exhaust gas streams in wallboard production are almost pure steam (moisture). For example, if an indirect kettle calciner is used for the production of stucco, the exhaust gases from the calciner is almost completely pure water vapor. This stream may be advantageously used as process gas for the activation step in the activated carbon production reactor.

Similar to the previous embodiment of the co-production of activated carbon and ethanol, the following advantageous aspects are included in the preferred embodiments of co-production of activated carbon and gypsum wallboard.

(i) Cooling of hot activated carbon product with moisture-rich gases from wallboard manufacturing

(ii) Use of moisture-rich exhaust gases from the wallboard manufacturing as process feed gas for carbon activation in the activated carbon production reactor

• Removal of SO₂ generated from the combustion of product gas from the activated carbon production reactor

In another embodiment of the invention, if the combined activated carbon and wallboard plant is located at a coal-fired power plant equipped with a wet flue gas desulfurization scrubber making gypsum for supply to the wallboard plant, the lime/limestone slurry from the coal-fired plant's scrubber system may be advantageously pumped via pipe-line to the wallboard production section of the co-production plant. A wet scrubber system may be employed to remove SO₂ from the process gases generated from the combustion of the hydrogen-rich product gas from the activated carbon production reactor using the lime/limestone slurry from the coal- fired power plant. The "used-up" slurry can be returned to the coal-fired plant wet scrubber system for additional processing (for example, oxidation to gypsum and separation). In this manner, capital equipment required for scrubbing SO₂ from the gases generated from the combustion of product gases can be minimized as the feed lime/limestone preparation and "used scrubber liquid" handling can be performed in an efficient manner with the coal-fired scrubber system.

Example

Integrated Wallboard and Activated Carbon Production Plant

An integrated wallboard and activated carbon production plant with the identified improvements (Figure 4, 5 and 6) and advantages relative to stand-alone plants is described below.

Coal (lignite) of the composition identified in previous examples is used as feed stock. The production of process heat for drying the raw "wet" gypsum feed section of the process is performed in the following manner (Figure 5). About 5000 kg/hour of coal is introduced into a multiple hearth furnace. About 8000 kg/hour air and 3500 kg/hour steam is introduced in the various hearths of the MHF to generate the heat required and provide the optimum gaseous environment for the production of activated carbon. About 1000 kg/hour of activated carbon is produced from this reactor set-up. The hot combustible product gases leaving the multiple hearth furnace (activated carbon production reactor) at the top is sent to the gypsum dryer burner in the wallboard plant. Additional air is added to the burner (Air-2 - 7300 kg/hour) to completely combust the hydrocarbons to yield an approximately 1900⁰C hot gas. This is mixed with the cold exhaust to generate process hot gas of at about 78,700 kg/hour at 53O⁰C. The amount of heat supplied by this hot gas is sufficient to dry 124 short tons per hour of approximately 10% moisture raw gypsum feed.

The production of process heat for the gypsum calcining section is performed in the following manner (Figure 6). An additional of about 6550 kg/hour of coal is introduced into the multiple hearth furnace along with about 10000 kg/hour air and 4600 kg/hour steam to produce an additional 1350 kg/hour of activated carbon from this reactor set-up. The hot combustible product gases leaving the multiple hearth furnace at the top is sent to the gypsum calciner burner in the wallboard production section of the co-production plant. Additional air is added to the burner (Air-2 - 10000 kg/hour) to completely combust the hydrocarbons to yield an approximately 1900⁰C hot gas. This is mixed with the cold exhaust to generate process hot gas of at about 99,000 kg/hour at 56O⁰C. The amount of heat supplied by this hot gas is sufficient to calcine 108 short tons per hour of dry gypsum feed to yield 91 short tons of stucco.

The activated carbon production reactor can be sized to provide enough combustible process gas for feed drying, calcination and board drying steps of wallboard production - and splitting the product gas to direct to each end application. IV. Co-Production of Activated Carbon and Cement:

Cement manufacturing generates about 2 tons of CO₂ for every ton of cement clinker of produced. Half of the CO₂ produced is from the combustion of the fuel required for the clinkering and calcination process. There is a need to reduce CO₂ emissions from cement clinker manufacturing.

In this embodiment (Figure 7), activated carbon and cement/lime is co-produced in the co-production plant (140). The combustible product gases from the activated carbon production reactor (26) from the activated carbon manufacturing section of the plant (20) are directed to the cement manufacturing section of the plant (150). There, the combustible gases are advantageously combusted in either the cement clinkering kiln or in the pre-calciner section (154) (Figure 7), with the energy used to calcine limestone (CaCO₃) to lime (CaO). The combustible gases are advantageously combusted in a burner (152) prior to or while contacting the limestone. In this manner, a lower carbon/hydrogen ratio fuel is used for process heat compared to the entire coal thus reducing the overall CO₂ emissions from cement/lime manufacturing section (150). Again, as described in previous embodiments, the carbon-dioxide rich flue gases from cement manufacturing may be used as reaction process gas in the activation section of the activated carbon production reactor. If steam is required for activation instead of carbon dioxide, then a portion of the energy in the hydrogen-rich combustible gases may be advantageously used for steam generation in a boiler (152), which may be combined with the hydrogen-rich combustible gas burner. The exhaust from the calciner is typically at high temperatures and is typically cooled (for example, by water quench) in the gas cooler (156) before it is cleaned and exhausted.

The energy content in the coal used is about 6400 Btu/lb and the total energy content coming into the process with the coal is 300 MMBtu/hr (21,220 kg/h or 46,680 lb/h coal). The energy content leaving the process with the activated carbon is about 99 MMBtu/hr. The remainder is about 200 MMBtu/hr and is the energy content of the hydrogen-rich combustible gases. The amount of limestone calcined is 30,026 kg/h. The amount of energy required for limestone calcination (heating to 800⁰C and heat of calcination) is 75 MMBtu/hr which is about 38 percent of the energy content of the hydrogen-rich combustible gases. The energy required for water evaporation for the process (activation) corresponds to about 14,854 kg/h (32,700 lb/h) or about 33 MMBtu/hr. This corresponds to another 16 percent of energy utilization or a total of about 50 percent utilization of the energy in the hydrogen-rich combustible gases. This process example has a lower utilization efficiency compared to previous examples because the heat delivery has to occur at a high process temperature (800⁰C for calcination).

With respect to the above description then, it is to be realized that the optimum relationships for the elements of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed apparent to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.

Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

What is claimed is:

Claims

1. A method comprising: providing a parent hydrocarbon-rich material; processing the parent material so as to produce both a carbon-rich solid material that has a higher carbon to hydrogen ratio that that of the parent material and a hydrogen-rich combustible gas that has a lower carbon to hydrogen ration than the parent material, the process comprising activating the material by exposing it to a hot gas stream comprising elevated levels of one or both of carbon dioxide and water vapor; combusting the combustible gas to produce heat; and using at least about 40% of the energy content of the combustible gas in a separate process comprising at least one endothermic step.

2. The method of claim 1 wherein the endothermic step comprises generating electricity.

3. The method of claim 2 in which the electricity is generated by using the heat to produce steam that is used to drive a turbine.

4. The method of claim 3 further comprising using the steam leaving the turbine in a heating or drying step in the separate process, thereby using at least about 70% of the energy content of the combustible gas.

5. The method of claim 2 in which the electricity is generated by a gas engine or other device, and the hot exhaust from such a device is used to generate steam that is used in the separate process.

6. The method of claim 1 wherein the endothermic step is a step of a separate process selected from the group of separate processes including ethanol production, paperboard production, gypsum wallboard production and cement production.

7. The method of claim 6 further comprising adding supplemental fuel to the combustible gas before the combusting step, to more closely meet the thermal needs of the separate process.

8. The method of claim 1 in which the endothermic step involves water evaporation or drying, material heating, or calcinations.

9. The method of claim 1 further comprising using the heat produced from combustion in a separate process comprising at least one endothermic step, the separate process resulting in part in a gas stream comprising elevated levels of one or both of carbon dioxide and water vapor, and then using the gas stream at least in part as either the hot gas stream for activation of the carbon- rich solid material, or to cool the carbon-rich solid material.

10. The method of claim 1 wherein the separate process comprises ethanol production.

11. The method of claim 10 wherein the heat is used to generate steam that is used in one or more endothermic steps of the ethanol production.

12. The method of claim 11 further comprising adding supplemental fuel to the combustible gas before the combusting step.

13. The method of claim 12 wherein ethanol production results in the emission of volatile organic compounds (VOCs), wherein the at least some of the VOCs are used as a supplemental fuel.

14. The method of claim 10 wherein ethanol production results in the emission of volatile organic compounds (VOCs), wherein the at least some of the VOCs are combusted to produce heat used in the step of processing the parent material so as to produce both a carbon-rich solid material that has a higher carbon to hydrogen ratio that that of the parent material and a hydrogen-rich combustible gas that has a lower carbon to hydrogen ration than the parent material.

15. The method of claim 1 wherein the separate process comprises paperboard production.

16. The method of claim 15 wherein the heat is used to generate hot gas or steam that is used to dry the paperboard.

17. The method of claim 16 further comprising adding supplemental fuel to the combustible gas before the combusting step, to generate sufficient steam for paperboard production.

18. The method of claim 15 wherein the parent material comprises cellulosic waste from the paperboard production.

19. The method of claim 1 wherein the separate process comprises gypsum wallboard production.

20. The method of claim 19 further comprising adding supplemental fuel to the combustible gas before the combusting step.

21. The method of claim 1 wherein the separate process comprises cement production.

22. The method of claim 21 further comprising adding supplemental fuel to the combustible gas before the combusting step.

23. The method of claim 1 further comprising adding supplemental fuel to the combustible gas before the combusting step.

24. The method of claim 1 wherein the carbon-rich solid material comprises activated carbon with surface area of at least about 200 m²/gm.

25. The method of claim 24 wherein the carbon-rich solid material comprises activated carbon with surface area of at least about 400 m /gm.

26. A method comprising: a) providing a parent hydrocarbon-rich material; b) processing the parent material so as to produce both a carbon-rich solid material that has a higher carbon to hydrogen ratio than that of the parent material and a hydrogen-rich combustible gas that has a lower carbon to hydrogen ration than the parent material, the process comprising activating the material by exposing it to a hot gas stream comprising elevated levels of one or both of carbon dioxide and water vapor; c) combusting the combustible gas to produce heat; d) using the heat produced from combustion in a separate process comprising at least one endothermic step, the separate process resulting in part in a gas stream comprising elevated levels of one or both of carbon dioxide and water vapor; and e) using the gas stream at least in part as either the hot gas stream for activation of the carbon-rich solid material, or to cool the carbon-rich solid material.